Hydrotreating can include processes which convert hydrocarbons in the presence of hydrotreating catalyst and hydrogen to more valuable products.
Due to environmental concerns and newly enacted rules and regulations, saleable fuels must meet lower and lower limits on contaminates, such as sulfur and nitrogen. New regulations require essentially complete removal of sulfur from diesel. For example, the low sulfur diesel requirement is typically less than about 100 or 50 wppm sulfur. The ultra low sulfur diesel (ULSD) requirement is typically less than about 10 wppm sulfur.
Hydrotreating can be used to remove heteroatoms such as sulfur and nitrogen from hydrocarbon streams to meet fuel specifications and to saturate olefinic compounds. Hydrotreating can be performed at high or low pressures, but is typically operated at lower pressure than hydrocracking.
Hydrotreating recovery units typically include a single stripper for stripping hydrotreated effluent with a stripping medium such as steam to remove unwanted hydrogen sulfide. The stripped effluent then is heated in a fired heater to fractionation temperature before entering a product fractionation column to recover products such as naphtha, kerosene and diesel.
Hydrotreating is very energy-intensive due to the severe process conditions such as the high temperature and pressure used. When hydrotreating vacuum gas oil (VGO), significant amount of fuel is consumed in the feed heater to the product fractionator to separate a diesel product stream from a treated VGO product stream. For a typical VGO hydrotreating unit, the feed heater to the product fractionator may be responsible for about 42% of total utility cost.
There is a continuing need, therefore, for improved methods of recovering fuel products from hydrotreated effluents. Such methods must be more energy efficient to meet the increasing needs of refiners.